Adhesive applying machines have been known for many years. The devices of interest are used for applying a thin layer or film of adhesive on the back of a sheet material such as a photograph, illustration, or the like, for adherence to a larger sheet. Typically, such devices are employed to facilitate the "lay-out" or editing of printed publications and similar materials. The most prominent unit of this nature in use today is that taught by U.S. Pat. No. 3,752,114 for ADHESIVE APPLYING MACHINE, assigned to the assignee of the instant application.
While extremely successful in the market due to its utility, the prior art adhesive wax applying machines have a number of associated shortcomings. Specifically, the prior art devices do not include a positive on/off switch to control the heating element, but a rheostat switch which includes no readily observable indicia that the heating element is on or off. Further, the prior art adhesive applying machines include a motor for controlling the drive of a pair of rollers for applying the adhesive, but the control of the motor is independent of the heater. Accordingly, the motor can be actuated without the adhesive wax being melted, the result being an overload to the motor. Further, if the wax is not sufficiently heated, or heated to a state of pure liquid, globules of adhesive can attach to the roller and to the article to which the adhesive is to be applied. As a result, lumps or the like are present on the sheet material to which the adhesive is applied. Worse yet, the globules may pass from the adhesive applying roller to the pressure roller, the result being the transfer of adhesive from the pressure roller to the face surface of the sheet to which the adhesive is to be applied. The prior art provides no means for assuring that operation of the machine can only occur after the wax has achieved a preferred temperature level to prevent such globules, assure the transfer of a uniform layer of adhesive, and reduce wear on the motor and drive mechanism.
Further, the motor control switch of the prior art does not include any visual indicia of the state of actuation of the switch, the motor often times inadvertently being left in a running condition.
The prior is was further devoid of a plurality of thermal fuses or thermal cutoffs to shut down the system if the wax or wax pan were to overheat. While the prior art has taught the implementation of a single thermal fuse for such purposes, no redundancy for such failures has been provided.
Additionally, the prior art teaches that the interconnection between the motor and drive roller could be achieved by a simple O ring. However, such O ring is given to slippage and wear, requiring frequent replacement and often being ineffective for properly driving the roller to effectuate a desired bite between the pressure roller and adhesive roller.